Sunday, May 11, 2025
5/11/2025
Modulation of OPRM1 alternative splicing by morphine and HIV-1 Nef - PROJECT SUMMARY This R01 application is in response to PAS-18-915 entitled “HIV/AIDS High Priority Drug Abuse Research”. Our project will investigate the molecular and functional interactions between HIV and morphine in regulation of alternative pre-mRNA splicing of the opioid receptor M1 (OPRM1) with implications for enhanced opioid dependence observed in the people with HIV (PWH). Clinically used opioids, such as morphine, as well as illicit drugs, such as heroin, activate OPRM1 that is a member of the G protein-coupled receptor (GPCR) family. OPRM1 pre-mRNA undergoes extensive alternative splicing events. To date, 21 isoforms of the human OPRM1 with alternative C-terminal and/or N-terminal regions and 17 isoforms of the rat OPRM1, have been identified. Given the importance of these regions in G protein-coupled receptor (GPCR) signaling, differential regulation of OPRM1 isoforms would have functional consequences. However, characterization of OPRM1 signaling is generalized, and only one isoform (MOR1) has been extensively studied. Our preliminary data suggest that expression of splicing regulatory protein SRSF1 and alternative splicing of MOR-1X is preferentially induced in neuronal cells exposed to morphine. Interestingly, our results also revealed that alternative splicing and expression of MOR-1X isoform is induced in postmortem brain tissues obtained from the PWH. These results suggested that HIV and morphine may impact OPRM1 alternative splicing and synergistically induce MOR-1X isoform expression. The mutually exclusive exon X of OPRM1 pre-mRNA is incorporated into the mature mRNA transcript following exon 3 in the MOR-1X mRNA transcript. This insertion results in substantially longer C-terminal tail having new motifs potentially binding with several cellular kinases that is unique to the MOR-1X isoform. We recently reported that glial cells infected with HIV-1 release Nef protein captured within the extracellular vesicles (Nef-EVs) which are readily taken up by neurons. We further assessed possible role of Nef-EVs and two other HIV secretory proteins, Tat and gp120, in alternative splicing of MOR-1X. Interestingly, while recombinant Tat and gp120 had no visible effects, treatment of neurons with Nef-EVs caused a comparable induction in MOR-1X alternative splicing as did treatment with morphine. Our preliminary results also revealed that co-treatment of neurons with Nef-EVs and morphine synergistically induced MOR-1X alternative splicing. Additionally, alternative splicing of MOR-1X was induced in brain regions involved in the reward pathways of the F344 rat that is the control strain of HIV-1Tg rat that has an additive induction with the exposure to morphine. Taken all together, we hypothesize that HIV-1 contributes to the increased rate of opioid dependence in the PWH by amplifying the rate of MOR-1X alternative splicing induced by morphine. Our proposed studies will reveal a novel synergistic interaction between morphine and HIV on alternative splicing of OPRM1 pre-mRNA leading to preferential expression of MOR-1X isoform with implications in physical dependence of morphine.
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